1. Field of the Invention
The present invention relates to balance rings for motors, wherein a motor is equipped with a balance ring to provide a downward balancing and positioning force to a rotor of the motor during rotation of the rotor.
2. Description of the Related Art
U.S. Pat. No. 6,050,785 to Horng issued on Apr. 18, 2000 discloses a miniature heat dissipating fan assembly including a casing, a circuit board, a balance plate, a stator, a rotor, and a cover plate. The balance plate is made of magnetic material and mounted around a tube seat on the casing and below the rotor. A permanent ring magnet on the rotor and the balance plate attract each other to generate an attraction therebetween for creating a balancing force for assuring stable rotational movements of the rotor relative to the stator, thereby eliminating noise resulting from vibrations during rotation of the rotor. U.S. Pat. No. 6,097,120 to Horng issued on Aug. 1, 2000 discloses a brushless D.C. motor assembly including a balancing sheet made of material with magnetic conductivity, the balancing sheet having an axle hole joined together with a stator by an axle tube, a rotor rotatably received in the axle tube, the rotation thereof controlled by a controlling device, and the rotor having an annular permanent ring magnet with a diameter substantially the same as that of the balancing sheet wherein the permanent ring magnet and the balancing sheet attract with each other. It was, however, found that the balancing and positioning effect for the rotor was still unsatisfactory.
It is the primary object of the present invention to provide a motor with a balance ring that may provide a relatively large magnetic attraction area between the balance ring and a rotor of the motor, thereby providing the best positioning and balancing effect for the rotor during rotation of the rotor.
A motor in accordance with the present invention comprises a base plate with an axle seat to which a stator bobbin is mounted. The stator bobbin comprises an axle hole for rotatably receiving a shaft of a rotor. The rotor comprises a permanent ring magnet. A balance ring is mounted to the base plate and comprises an upright annular wall and an annular bottom wall. The upright annular wall of the balance ring and a lower section of the permanent ring magnet attract each other while the annular bottom wall of the balance ring and a lower end face of the permanent ring magnet attract each other.